Rocket propulsion method



July 7,1959

D. R. CARMODY ETAL ROCKET PROPULSION METI-iOD Filed Jan. 4, 1954 OX/D/ZER INVENTORS: A/ex Z/fz 000 R. Carmady Evan A. Mayer/q 27 my 6 vvi dswe Pat Alex Zletz, Park Forest, 111,, assignors to Standard Oil Company, Chicago, 11]., a corporation of Indiana Application January 4, 1954, Serial No. 402,186

' reclaims. 11. 60 35.4

This invention relates to the generation of gas. 'More particularly it relates to a method of reaction propulsion by the hypergolic reaction of a nitric acid oxidizer and a liquid fuel. 7 r 7 Reaction propulsion or rocket propulsion operates with a fuel system that is not dependent on atmospheric oxygen. The fuel system may consist of a single selfcontained propellant, i.e., mono propellant system or it may consist of a' separate fuel and a separate oxidizer, i.e., bi-propellant'system. 7 a

A bi-propellant rocket carries 'the fuel and the oxidizer in separate tanks. The fuel andthe oxidizer are intro duced separately and substantially simultaneously into the combustion chamber of the rocket motor. The gaseous products .of the reaction. of the. fuel and the oxidizer are discharged through an exit nozzle; the forwardlthrustis developed-by.the passage of thesegaseous products through the nozzle. A self-igniting fuel system is preferred because of the possibilities of failure when using auxiliary methods of ignition, :such as a spark plug or a glow plug. A fuel which js s'elfd'gniting or spontaneously combustionable when contacted with an oxidizer is known as a hypergolic fuel. Temperature-has an important bearingon the hypergolic activity of fuels. The earthsgsurface may vary in temperature from a high of about-+125 -F. to a low of about 65 F. Temperature fbelowjabout 30? F. are exceptional. Surface-to-air missiles orrocket driven aircraft must be capable of operation at temperatures on 1115011181 (if-30 F.; this means that a hypergolic reaction must take place when the temperature of the fuel and. the oxidizer at the moment of initial contact in the combustionrch'amber are at a temperature of about --3'() F. High altitude temperatures are normally on the order of 65- Fkand lare known to reach: 1'00 F. An air-tQ-air missiIe must be able to operate at these very low atmospheric" t'einperatu'resj that is, the fuel and the oxidizer must reacthyperg olically even though at the moment of initial contacting in the combustion chamber of the rocket motor they are at a temperature of about --6 F. or even lower. An object of the invention is a method of generating gas by the hypergolic reaction of a fuel and a nitric acid oxidizer. Another object is a method of reaction propulsion or rocket propulsion by the use of the hypergolic reaction of a fuel and a nitric acid oxidizer. Stillanother object is a'method of rocket propulsion by the use of the hypergolic reaction of a nitric acid oxidizer and a fuel which containsj appreciable amounts of hydrocarbons, which hydrocarbons are essentially non-hypergolic, at ordinary temperatures. Yet another object is a novel class of organic compounds. Other objects will become apparent I inthe course of thedet ailed description of the invention. The novel compositions havingthe general formula R NP (OR), wherein R isselected fromthe class consisting of alkyl and 'alkenyl and the' total number of carbon atoms in the composition is not more than 16, and

preferablynot more than 5' carbon atoms are present in any R group, undergoes a hypergolic reaction with nitric acid oxidizers at atmospheric temperatures to produce gaseous products of decomposition. This fuel can be used in rocket propulsion by injecting the fuel and a nitric acid oxidizer separately and substantially simultaneously into the combustion chamber of a rocket motor and discharging the gaseous decomposition products from said combustion chamber through an exit nozzle.

The compositions of this invention are hypergolic with nitric acid oxidizers at ordinary temperatures, such as about F. At temperatures on the order of 0 F., a hypergolic reaction takes place with nitric acid oxidizers containing as much as 5 weight percent of non-acidic materials. The non-acidic materials generally are used to depress the freezing point of high purity nitric acid. The most common materials are water itself or aqueous solutions of potassium nitrite or nitrate. These nonacidic materials have an adverse influence on the hypergolic activity of the nitric acid and therefore nitric acid containing large amounts of these materials cannot be used at very low atmospheric temperatures. Commercial grade white fuming nitric acidWFNAwhich contains about 2 percent of water can be used down to its freezing point of about 40 F. WFNA is the preferred oxidizer at temperatures above its freezing point. Red fuming nitric acid, which consists of nitric acid and dissolved N O is usable over the entire range of atmospheric temperatures. In general, RFNA contains 7 percent or more of N 0 For operation at very low atmospheric temperatures, i.e., below about 65 F., the preferred oxidizer is RFNA containing at least about 16 percent of N204.

, Nitric acid oxidizers suitable for use at very low temperatures can be obtained by mixing with various strong oxidizing acids. A suitable nitric acid oxidizer consists of WFNA and oleum. Oleum consists of sulfuric acid and dissolved S0 A blend containing about percent of WFNA and about 20 percent of oleum containing about 10 percent of S0 is suitable for use at temperatures on the order of -65 F. Blends of WFNA and alkanesulfonic acids containing not more than 4 car'- bon atoms in the alkane group are particularly suitable for use at very low atmospheric temperatures. For example, a.blend consisting of percent WFNA and 15 percent methanesulfonic acid is usable at temperatures of -73 F.; a blend consisting of 84 percent WFNA and 16 percent ethanesulfonic acid is usable at temperatures of 64 F.

It is to be understood that while all nitric acid oxidizers are not suitable for use over the entire range of atmospheric temperatures, the term nitric acid oxidizer is intended to include those oxidizers which are suitable at the desired temperature of initial contacting of the fuel and the oxidizer.

The novel fuel of this invention has the general formula.R- NP(OR) wherein R is selected from the class consisting of alkyl and alkenyl and the total number of carbon atoms in such fuel is not more than 16. This composition is designated hereinafter, as mono- (dialiphaticamino)-dialiphaticphosphite wherein the total number of carbon atoms is not more than 16 and the aliphatic groups are selected from the class consisting of alkyl and alkenyl. It is preferred that not more than 5 carbon atoms be present in any aliphatic group. Examples of the alkyl derivatives are mono(dimethylamino) dimethylphosphite, mono(dimethylamino) di-n-propylphosphite, mono(di-n-butylamino) di-n-propylphosphite and mono(diethylamino)-dimethylphosphite. For very low temperature operation the compositions containing methyl groups, ethyl groups and mixtures thereof are preferred.

The phosphite compositions can be blended with essentially non-hypergolic liquid hydrocarbons to produce hypergolic fuels that are useful for gas generation or rocket propulsion. An essentially non-hypergolic liquid hydrocarbon is defined as one that does not react with a nitric acid oxidizer to produce a visible flame, although gaseous products may be produced, at ordinary temperature, i.e., at about 80 F. Examples of these essentially nonhypergolic liquid hydrocarbons are heptane, octane, heavy naphtha, kerosene, jet plane fuel, diesel oil, cracked naphtha, di-isobutylene, propylene tetramer, and butylene trimer. I

At ordinary temperatures, blends of saturated hydrocarbons, i.e., paraffins and cycloparafiins with the defined phosphites possess, in general, hypergolic activity substantially equal to blends of the defined phosphites and unsaturated hydrocarbons such as olefins and cycloolefins. The low temperature activity of the two blends is surprisingly different. Blends of the defined phosphites and olefins containing from about 7 to about 20 carbon atoms are much more active at low temperature than are the corresponding saturated hydrocarbons. The olefin polymers made by polymerizing butylenes or propylenes and co-polymerizing butylenes and propylenes are particularly suitable essentially non-hypergolic liquid hydrocarbons.

In general, the mixed fuel of this invention consists essentially of between about 25 and 75 volume percent of the defined phosphite and the remainder an essentially non-hypergolic liquid hydrocarbon; preferably, an olefin containing between about 7 and 20 carbon atoms. For operation at very low atmospheric temperatures, it is preferred to use a fuel consisting essentially of about equal volumes of an olefin polymer containing about 8 carbon atoms and the defined phosphite containing methyl groups only, ethyl groups only, or a mixture of methyl and ethyl groups.

The novel compositions of this invention and the results obtainable therewith are set out in the following illustrative examples.

The ignition delays set out below were determined by means of an apparatus which permitted the measurement of the delay in milliseconds. (The ignition delay is defined as the time between the mixing of the fuel and the oxidizer and the appearance of a visible flame.) The delays were determined by cooling the fuel and the oxidizer separately to the desired temperature and introducing these into the apparatus which had also been cooled to the desired temperature. The WFNA used in the examples contained about 2 weight percent of water. The RFNA used in the examples contained about 22 weight percent of N Example I Mono(dimethylamino)-di-n-propylphosphite was prepared as follows: Phosphorus trichloride was reacted with l-propanol in pentane solution. The HCl formed in the reaction was removed with dimethylaniline. The amine salt was removed by. filtration and the pentane was distilled from the reaction mixture.

The pentane-free reaction product mixture was carefully distilled under vacuum. Two fractions distilling between 115 to 130 C. and 130 to 150 C. at 120 mm. were used for the subsequent reaction. These two fractions represented about 30% of the theoretical yield of di-n-propyl chlorophosphite.

The chlorophosphite was dissolved in pentane and reacted with a very large excess of dimethylamine. The amine hydro chloride formed by reaction of the excess amine with the HCl was removed by filtration. Pentane was stripped from the filtrate and the reaction product mixture distilled under vacuum. The yield of the fraction identified as mono(dimethylamino')--di-n-propylphosphite was about 76% of theory.

The product was subjected to ultimate analysis. The composition as calculated on the basis that the compound was mono(dimethylamino)-di-n-propylphosphitc is compared below with the analytical results.

Actual, Theoretical, percent percent Carbon 59. 5 60.6 Hydrogen-- 11. 7 11. 6 Oxygen-... 9. 5 11.5 Nitrogen... 4. 9 5. l Phosphorou 11.0 11. 2

The physical characteristics of mono(dimethylamino)- di-n-propylphosphite are:

Boiling point, C 88-905 at 18 mm. Melting point Below F. Density, g./ml. at 20 C 0.935.

Refractive index, 20 C 1.4379.

The ignition delays of this compound were determined at various temperatures and are set out in the following tabulation:

Ignition Temperature Oxidizer delay, milliseconds RFNA.... 5.3.8

Example II Actual Theoretical, percent percent Carbon 51. 3 49. 7 Hydrogen- 10. 6 10. 4 Oxygen. 17. 1 16. 6 Nitrogen 5. 6 7. 2 Phnenhnmns 14. 8 16. D

The physical properties of mono(di-n-butylamino)-din-propylphosphite are:

Boiling point, C. 905-100 at 0.3 mm; Melting point Below .-100" F. Density, g./ml. at 20 C 0.900. Refractive index, 20 C 1.4444.

The ignition delays of this compound at various temperatures are set out in the following tabulation:

Temperature Oxodizer Ignitiondeley,

milliseconds WFNA.-- 49.8. RFNA---- 1.5. WFNA-.. 69.4. RFNA No ignition For low temperature operation an ignition delay of about 100 milliseconds is acceptable. These data indicate that this compound, which contains 14 carbon atoms, is acceptable when used with white fuming nitric acid oxidizer.

Example Ill Mono(dimethylamino)edimethylphosphite was prepared in a manner similar to that set out in Example I, except that sodium methylate 'wa'sjis'ed instead'of the methanol and no dimethyl aniline was used. By the use of the sodium methylate, good yields of the desired'chlorophosphite were obtainable. The physical: characteristics of the mono(dimethylamino)-dimethy1phosphite are:

Boiling point, C. 82-90 at 120 mm. Melting point Below --100 F. Density, g./ml. at 20 C 0.963.

Refractive index, 20 C 1.4422.

This compound is very fluid at l00 F. It supercools easily and remains fluid at temperatures far below -100 F.

The ignition delays obtained at various temperatures with this compound are set out below:

Temperature Oxidizer Ignition delay,

' milliseconds 75 WFNA.- 7.7 75 F RFNA 10. 6 40 F WFN 15. 6 40 F RFNA 17. 7 65 F RFNA 19.3 -100 F RFNA 22. 6

The defined aminophosphitesi'react more readily with white fuming nitric acid than they do with red fuming nitric acid. This characteristic is of considerable value since WFNA is a more desirable oxidizer than RFNA because of its lower volatility and greater ease of pumping.

.Example IV two blends at various temperatures are set out below:

Temperature Oxidizer n-Heptane Di-isobutyl- Blend ene Blend The mixed fuels Were chilled in liquid nitrogen until they had attained a temperature well below 100 F. Both blends showed no phase separation, i.e., the two components are miscible at this low temperature. Both blends were extremely fluid at these temperatures. The di-isobutylene blend is noteworthy in that the ignition delay at very low temperature is only slightly higher than the ignition delay of the aminophosphite itself.

The data of Example IV show that a mixed fuel can be obtained which has an ignition delay of below about 100 milliseconds, preferably 50 milliseconds, that is suitable for rocket propulsion purposes at very low atmospheric temperatures.

By way of illustration the composition of this invention is applied to the propulsion of an air-to-air missile. The annexed figure which forms a part of this specification shows schematically the bi-propellant fuel system, the motor and other parts of such a missile.

In the figure vessel 11 contains a quantity of gas at high pressure; this gas must be inert with respect to the oxidizer and the fuel; suitable gases are nitrogen and helium. Herein helium is used as the inert gas. Helium from vessel 11 is passed through line 12 and through valve 13 which regulates the flow of gas to maintain a constant pressure beyond valve 13. From valve 13 helium is passed through lines 14 and 16 into vessel 17 and simultaneously through line 18 into vessel 19.

Vessel 17 contains the oxidizer. Helium pressure forces the oxidizer out of vessel 17 through line 21 to valve 22. Valve 22 is a solenoid actuated throttling valve. Suitable electrical lines connect valve 22 to an electrical source and operating switch (not shown) at the control panel of the aircraft. The oxidizer is passed through line 23 and injector 24 into combustion chamber 26. Combustion chamber 26 is provided with an outlet nozzle 27. Vessel 19 contains the fuel. Vessels 17 and19 are constructed to withstand the high pressure imposed by the helium gas. The gas pressure forcesffuel from vessel 19 through line 28 to solenoid actuated throttling-valve, 29. Valve 29 is similarin construction and ,in actuation to valve 22. Thefuel is passed throughline. 31- and injector32 into combustion chamber 26.:

Valves 22 and 29 are' of such a size and setting that a predetermined ratio of Ioxidize'r-to-fuel is passed into combustion chamber 26. .-Injectors 24 and 32 are so arranged that the streams. of oxidizeriand fuel converge and contact each other forcibly, resulting me very. thorough intermingling of the fuel and the oxider.

The missile is launched by activating the solenoids on valves 22 and 29. In this-illustration 4.5 lbs. of 22% RFNA are introduced into combustion chamber 26 per pound of fuel. Herein the fuel consists of 45 volume percent of a mono(diethylamino)-diethylphosphite and 55 volume percent of the di-isobutylene. The oxidizer and the fuel react almost instantaneously upon contact in the combustion chamber; alarge volume of very hot gas is produced in the combustion chamber, which gas escapes through orifice 27. The reaction from this expulsion of gas drives the missile toward'its target.) 4 1 a The extremely good ignition delay. of these 'phosphites makes them'excellent igniterfuel's. -Where economy is desirable or high thrust is' necessary, themain fuel may be one of relatively low hypergolic activity but possessing high thrust. Examples of these fuels are turpentines and cracked naphthas. These fuels are relatively nonhypergoiic at very low atmospheric temperatures. However, once the combustion chamber of the rocket motor has been heated by the reaction of an oxidizer and a fuel, these relatively non-hypergolic fuels are able to maintain the reaction in the combustion chamber. The reaction is begun by passing into the combustion chamber an igniter fuel which is readily hypergolic at very low atmospheric temperatures. The igniter fuel and the oxidizer react to generate a large volume of those gaseous decomposition products which heat rapidly the combustion chamber. The main fuel is then injected into the hot combustion chamber and reacts under these conditions with the oxidizer to continue the gas generation. The flight of the missile is then determined by the thrust characteristics of the main fuel and the oxidizer. For example, in a small size ground-to-air missile only about a pint of igniter fuel is necessary.

It is to be understood that the fuel and the oxidizer must be contacted in a ratio suflicient to initiate the hypergolic reaction. And the ratio of fuel to oxidizer must be regulated at such a point to maintain the hypergolic reaction after it has begun. The ratio may vary over a relatively wide range, dependent on the type of fuel, the oxidizer and the initial temperature of contactlng.

Thus, having described the invention, what is claimed is:

1. A method for generating gas, which method comprises contacting, in a reaction chamber, a nitric acid oxidizer and a fuel having the general formula wherein R is selected from the class consisting of alkyl and alkenyl and the total number of carbon atoms in said fuel is not more than 16, under conditions of temperature and oxidizer/fuel ratio such that a hypergolic reaction occurs to produce gaseous decomposition prodnets.

2. A method of propelling a rocket, which method comprises bringing together separately and substantially simultaneously into the combustion chamber of a rocket motor, a nitric acid oxidizer and a mono(dialiphaticamino)-dialiphaticphosphite, wherein the aliphatic groups are selected'trom the class ofzalkyl and alkenyl and the total :numbero'f carbon atoms in said phosphite is not more than 16 in an amount and at a rate sufiicient to initiate =ahypergolic reaction and to support combustion of the fuel, and dischargin'gthe gaseous decomposition products from saidcornbustion'chamber'through an exit nozzle.

3. The method of claim'2'wherein said fuel is mono(dimethylamino)-dirnethylphosphite.

4. The method of claim 2 wherein said fuel is mono(dimethylarnino)dbmpropylphosphite.

5. The method of claim 2 wherein said fuel is mono(din-butylamino) -di-n-propylphosphite.

6. The method of claim 2 wherein said oxidizer is white fuming nitric acid.

7. The method of claim 2 wherein said oxidizer is red fuming nitric acid.

8. A method of initiating combustion in a rocket motor, which method comprises bringing together in the combustion chamber, a nitric acid oxidizer and mono(dimethylamino)-dimethylphosphite, wherein the relative amounts of oxidizer and fuel are SllffiCient to initiate a spontaneous-combustion of the fuel.

9. A method ofrocket propulsion, which method comprises bringing together separately and substantially simultaneously into the combustion chamber of said rocket motor a nitric acid oxidizer and a mixed fuel consisting essentially of (a) a monotdialiphaticamino)-dialiphaticphosphite containing not more than 16 carbon atoms and wherein said aliphatic groups are selected from the class consisting of alkyl and alkenyl, in an amount between about 25 and about volume percent and (b) the remainder an essentially non-hypergolic liquid hydrocarbon in an amount and at a rate sn'flicient to initiate a hypergolic reaction and to su port combustion of the fuel, and discharging gaseous decomposition products through an exit nozzle. 7

10. The method of claim9 wherein said hydrocarbon is an olefin containing between about 7 and 20 carbon atoms. I

11. The method of claim 9 wherein said hydrocarbon is diisobutylene.

12. A method of rocket propulsion, which method comprises bringing together separately and substantially simultaneously into the combustion chamber of a rocket motor, a nitric acid oxidizer selected from the class consisting of white fuming nitric acid and red fuming nitric acid and a mixed fuel consisting essentially of about equal volumes of (a) mono(dimethylamino)-dirnethylphosphite and (b) an olefin polymer containing about 8 carbon atoms, said oxidizer and said fuel being present in an amount sufiicient to initiate and to maintain the spontaneous combustion of said-fuel and discharging gaseous combustion products through an exit nozzle.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD FOR GENERATING GAS, WHICH METHOD COMPRISES CONTACTING IN A REACTION CHAMBER, A NITRIC ACID OXIDIZER AND A FUEL HAVING THE GENERAL FORMULA R2NP(OR)2 WHEREIN R IS SELECTED FROM THE CLASS CONSISTING OF ALKYL AND ALKENYL AND THE TOTAL NUMBER OF CARBON ATOMS IN SAID FUEL IS NOT MORE THAN 16, UNDER CONDITIONS OF TEM- 